Due to ever increasing device densities and shrinking feature dimensions, successful interconnect metallization has become very critical and challenging. Process engineers are faced with difficult topologies in ultra-large scale integrated (ULSI) circuit manufacturing. With shrinking design rules for ULSI circuits, obtaining adequate step-coverage on high aspect ratio contacts and vias has become critical.
In a majority of manufacturing lines, metallization engineers have utilized tungsten-plug technology followed by aluminum physical vapor deposition (PVD) for backend metallization. These steps have been adopted to take advantage of the excellent contact and via fill ability of the tungsten chemical vapor deposition (CVD) process. However, tungsten-plug technology has some significant deficiencies. See, for example, W. Robi, et al., Conference Proceedings ULSI XIII Materials Research Society, p. 251, 1998.
High contact and via resistance, and the cost associated with the tungsten-plug process have attracted metallization engineers to try alternative aluminum-based technologies for contact and via fill. These technologies offer the tremendous advantages of process simplicity and low cost. For the same reasons, other approaches such as a two-step cold/hot fill, forcefill technology, low-pressure deposition and aluminum low pressure seed (ALPS) technologies have also been investigated. See, for example, B. Zhao et al., IEEE IEDM, p. 353, 1996; J.-H. Yun, Appl. J. Phys., Vol. 40, p. 5105, 2001; T. Guo et al., Thin Solid Films, 332, p. 319, 1998; and G. Yao et al., Conference Proceedings ULSI XIII Materials Research Society, p. 243, 1998.
Via fill using a two-step cold/hot aluminum sputter metallization process depends on via density. Via fill using a two-step cold/hot aluminum sputter metallization process also depends upon the ratio of the cold deposition time to the hot deposition time. For a successful via fill, a conformal aluminum layer must be formed with the cold deposition process. The conformal aluminum layer acts as a seed and wetting layer to promote metal reflow during the subsequent hot deposition process. Insufficient cold deposition of the aluminum prevents hot reflow of the aluminum into the vias. Excessive cold deposition of aluminum creates voids and bridges across the via entrances.
There is a need in the art for a system and method that is capable of maximizing the number of successful via fills in aluminum multilayer metallization in a manufacturing process for a semiconductor wafer.